I don't have experience with pot metal repair but you are describing a soldering or brazing process (melting point of the rod being the only distinction).
I searched "low melt alloys for pot metal repair" and there are many advertised:
link to search results
Is there any way to identify the composition of the rod you are looking for? If so, you might find a direct alternative. If not, you can try some of those advertised.
Does your rod have a flux core or coating? I would expect you'd need an aggressive flux to solder pot metal but I'm just guessing.